APPARATUS AND METHOD FOR PREPARING AND SUPPLYING FUEL The present invention relates to the preparation and supply of fuel. More particularly, a method and apparatus in accordance with the present invention offers at least one capillary flow passage heated to vaporize fuel. The ability to produce finally atomized fluid spray is beneficial in many applications including the manufacture of substrates for industry, the feeding of fuel to combustion systems, including the fuel feeding of internal combustion and external combustion engines, the formation of particles of uniform size for the production of pharmaceutical products, the production of small particles for use as test standards and various applications in the electronics industry, where thin film deposition techniques are often used to form resistors, capacitors and other components . In general, the complete and clean character of the combustion of a liquid fuel depends on the fuel-air ratio, the mechanical and aerodynamic design of the combustion chamber, the type of fuel, the fuel injector design and the size distribution. of small drops of fuel. A primary objective in the design of fuel systems in recent years has been the reduction of emissions generated by combustion. This has been applied to a wide range of applications, from residential heating equipment to internal combustion engines for automobiles to gas turbines to industrial furnaces and utility facilities. The method of preparing liquid fuel has had a very important impact on the resulting emissions, especially carbon monoxide (CO), unburned hydrocarbons (HC) and soot emissions. Thus, in the quest to continuously reduce the emissions of devices that burn liquid fuels, an important effort has been made focused on developing simple and economical methods to achieve the supply of either vaporized fuel or very fine small drops of fuel. In any liquid fuel combustion application, reducing the size of small droplets can offer several benefits, including improved ignition characteristics, reduced contact of small droplets against the walls of the chamber, faster evaporation of small droplets of liquid, reduced emissions of CO, HC and soot, and the ability to operate with liquid fuels of lower volatility (or heavier). Even when a fuel can be supplied to a combustion chamber in the form of small liquid droplets, the liquid must be evaporated before the constituents of the fuel can react with the oxygen in the combustion air. Drops of larger size evaporate slowly and may not have the time to fully evaporate and react before leaving the combustion chamber, which causes higher levels of emissions. Particularly in the case of combustion systems on a very small scale (say less than 1020 kg-m / second (10 kW) of heat release), the importance of achieving very small droplet sizes is especially critical, especially in the case of lower volatility fuels such as diesel or jet fuel. In addition, these small-scale systems require simple fuel delivery systems that do not use large amounts of energy to prepare the fuel. Thus, conventional approaches to supplying the fuel (for example, atomization under pressure, atomization of double or duplex fluid, ultrasonic atomization) can not be applied to small-scale systems: the flow rates are too high, the drops are too large , the supply pressures required are excessively high or an additional atomization fluid is required. A) Yes, many small-scale combustion systems are limited to gaseous fuels. Numerous approaches to reduce the size of the fuel sprays provided have been proposed. For example, a combustion device wherein the fuel is atomized by an ultrasonic atomizing device is disclosed in U.S. Patent No. 5,127,322. In accordance with this patent, atomizers have been proposed where the fuel is supplied to a combustion chamber in small fine droplets to accelerate the vaporization of the fuel and to reduce the time required for regular combustion of the fuel. U.S. Patent No. 5,127,822 describes an arrangement in which it is intended to supply the fuel at 5 cc / min and it is said that the fuel is atomized into small droplets having a Sauter Mean Diameter (SMD) of 40 um. Other atomization techniques are proposed in U.S. Patent Nos. 6,095,436 and 6,102,687. An ultrasonic atomizer contemplated to supply fuel to an internal combustion engine is proposed in U.S. Patent No. 4,986,248. US Patent 4,013,396 proposes an aerosol forming apparatus for a fuel, wherein a hydrocarbon fuel (eg, gasoline, fuel oil, kerosene, etc.) must be supplied to a condensation area to form a fuel in gasoline of which it is said to have small drops of relatively regular size less than 1 um in diameter. The aerosolized fuel is contemplated for mixing with the air to provide a desired air-fuel ratio and is burned in the combustion area of a burner combustion area of a burner. A heat exchanger is proposed to transfer heat from the burnt fuel to a medium that conveys heat such as air, gas or liquid. In U.S. Patent No. 5,472,645, a fuel vaporization device is proposed to solve certain problems related to incomplete combustion of fuel aerosols in internal fuel engines. According to U.S. Patent No. 5,472,645, since small drops of aerosol fuel do not ignite or burn completely in internal combustion engines, unburned fuel residues escape from the engine as contaminants, such as hydrocarbons (HC). , carbon monoxide (CO), and aldehydes with concomitant production of nitrogen oxides (N0: <;). U.S. Patent No. 5,472,645 proposes to improve the combustion of aerosol-type fuels by breaking up the liquid fuel in a stream of air and fluid from vaporized or gas phase elements. These elements are said to contain certain non-vaporized aerosols of higher molecular weight hydrocarbons with the lighter fuel components rapidly evaporating to the gas phase, mixing with the air and feeding to an internal combustion engine. The heavier fuel portion is transorbed in a vaporized state in the gas phase before it can leave a cyclone vortex device and enter the engine intake manifold. U.S. Patent No. 4,344,404 proposes an apparatus for supplying small drops of aerosolized fuel mixed with air to an internal combustion engine or burner, the small fuel droplets having sizes of 0.5 to 1.5 um. The liquid fuel in aerosol form is mixed with the air in an air-fuel ratio of approximately 18: 1, with the objective of reducing the levels of CO, HC and NO: c emissions of the engine. Several patents disclose techniques for vaporizing a liquid. For example: the US patents Nos. 5,743,251 and 6,234,167 disclose aerosol generators that vaporize a liquid in a heated capillary tube; US Patent No. 6,155,268 issued to Takeuchi discloses a liquid flavor supplied by capillary action through a flow passage to a heater placed at one end of the flow passage to vaporize the liquid flavor; U.S. Patent No. 5,870,525 issued to Young discloses that the liquid in a reservoir can be fed through a supply wick by capillary action to a boiler wick where the liquid is heated and boiled to the formation of a vapor; and US Pat. No. 6,195,504 issued to Horie et al. discloses heating a liquid in a flow passage to produce a vapor. U.S. Patent No. 3,716,416 discloses a fuel introduction device contemplated for use in a fuel cell system. ? 1 fuel cell system is contemplated to be self-regulating, producing energy at a predetermined level. The proposed fuel introduction system includes a capillary flow control device for throttling the fuel flow in response to energy production from the fuel cell, rather than providing an improved fuel preparation for subsequent combustion. On the contrary, the fuel is contemplated to be fed to the fuel cell for conversion to? .2 - a preferred embodiment, the capillary tubes are made of metal and the capillary itself is used as a resistor, ce is in electrical contact with the outlet of energy from the fuel cell. Since the resistance to the flow of a vapor is greater than the resistance to flow of a liquid, the flow is strangled as the power output rises. The fuels suggested for use include any fluid easily transformed from a liquid phase to a vapor phase by the application of heat and flowing freely through a capillary. Vaporization seems to be achieved in such a way that steam blockage occurs in automobile engines.
US Pat. No. 6,276,347 proposes a supercritical or quasi-supercritical atomizer and a method for achieving atomization or vaporization of a liquid. The supercritical atomizer of US Patent No. 6,276,347 allows the use of heavy fuels to ignite spark ignition piston engines, with low compression ratio, light, small that typically burn gasoline. The atomizer is contemplated to create a spray of small fine droplets from liquid fuels or liquid-type fuels by displacing the fuels to their supercritical temperature and releasing the fuels in a lower pressure region in the gas stability field in the phase diagram associated with the fuels, causing a fine atomization or vaporization of the fuel. Utility is disclosed for applications such as fuel engines, scientific equipment, chemical processing, waste disposal control, cleaning, chemical attack, insect control, surface modification, humidification and vaporization. To minimize decomposition, US Pat. No. 6,276,347 proposes maintaining the fuel below the supercritical temperature until the passage of the distal end of a restrictor for atomization. In the case of certain applications, heating only the tip of the restrictor is desirable to minimize the potential for chemical reactions or precipitation. It is said that this reduces the problems related to impurities, reagents or materials in the fuel stream that otherwise tend to be expelled from the solution, blocking the lines and filters. Working at supercritical temperatures or near supercritical temperatures suggests that the fuel supply system operates in a range of 21.1 to 56.2 kg / cirr (300 to 800) psig. While the use of supercritical pressures and supercritical temperatures can reduce the clogging of the atomizer, it seems to require the use of a relatively more expensive fuel pump, as well as a fuel line, attachments and the like that can operate at these high pressures. One aspect of the present invention is directed to an apparatus for vaporizing a liquid fuel taken from a liquid fuel source, comprising; (a) at least one capillary flow passage, said at least one capillary flow passage having an inlet end and an outlet end; (b) a fluid control valve for positioning said inlet end of said Lj.cs at a capillary flow passage in fluid communication with the liquid fuel source and for introducing the liquid fuel in a substantially liquid state; (c) a heat source positioned along said at least one capillary flow passage, said heat source operates to heat the liquid fuel in said at least one capillary flow passage at a level sufficient to change so minus a portion thereof from the liquid state to a vapor state and supplies a substantially vaporized fuel stream from said outlet end of said at least one capillary flow passage; Y
(d) a device for cleaning deposits formed during the operation of the apparatus. In another aspect, the present invention focuses on a method of vaporizing fuel, comprising the steps of:
(a) supplying liquid fuel to at least one capillary flow passage; (b) causing a substantially vaporized fuel stream to pass through an outlet of the at least one capillary flow passage by heating the liquid fuel in the at least one capillary flow passage; and (c) periodically cleaning the at least one capillary flow passage. The invention is further explained in the following description with reference to the drawings illustrating, by way of non-limiting examples, various embodiments of the present invention wherein: Figure 1 is a simple capillary fuel injector that can be cleaned in situ, in partial court; Figure 2 shows an array of multiple capillaries that can be used to implement the system shown in Figure 4; Figure 3 shows an end view of the device shown in Figure 2; Figure 4 shows details of a system that can be used to oxidize deposits in a multiple capillary array that can be used to supply vaporized fuel according to the invention; Figure 5 shows a scheme of a control system for supplying fuel and optionally oxidizing gas to a capillary flow passage; Figure 6 shows a schematic of an arrangement for using fuel heat to preheat the liquid fuel; Figure 7 is another simple capillary fuel injector, capable of cleaning in situ by abrasion the deposits formed there, in partial cut; Figure 7A is an enlarged cross-sectional view of the capillary fuel injector of Figure 7; Figure 8 presents a graph of the fuel flow rate vs time for a gasoline without additives, demonstrating the benefits of oxidation cleaning; Figure 9 is a graph of the fuel flow rate vs. time in the case of commercial grade gasoline; Figure 10 presents a graph of fuel flow rate vs time comparing several gasolines; Figure 11 is a graph of fuel flow rate vs time comparing an aircraft fuel with a No. 2 diesel fuel; Figure 12 presents a graph of a fuel flow rate vs. time for a diesel fuel without additives that shows the effect of rust cleaning; and Figure 13 is a graph of fuel flow rate vs time comparing a diesel fuel without additives with a diesel fuel containing an anti-fouling additive. Reference is now made to the embodiments illustrated in Figures 1-13 where the same reference numbers are used to refer to the same parts throughout the document. The present invention offers a useful fuel supply arrangement with virtually any application that requires an atomized or vaporized liquid fuel stream. The liquid fuel can be any type of hydrocarbon fuel such as aircraft fuel, gasoline, kerosene or diesel fuel, as well as oxygenates such as methane, ethanol, methyl tertiary butyl ether and mixtures of hydrocarbon and oxygenated fuels. The fuel supply arrangement includes at least one capillary flow passage that can heat liquid fuel such as vaporized fuel or a vaporized fuel mixture and optionally another fluid can be supplied to the application for subsequent combustion. Alternatively, the vaporized fuel may optionally be mixed with another fluid such as water or steam and supplied to a fuel reformer or processor. Advantageously, the fuel preparation and delivery apparatus of the present invention can operate with very short heating time and low energy requirement. When engines using conventional fuel systems are started, since little vaporization of the liquid fuel is properly effected, it is necessary to provide an excess of liquid fuel to the application in order to achieve an air-fuel mixture that ignites easily. This over-fueling typically results in undesirable exhaust emissions, including carbon monoxide, and unburned hydrocarbons. The degree of overfeeding of fuel is typically increased at lower engine starting temperatures, thereby increasing the exhaust emissions produced during start-up. The apparatus and method of the present invention can directly or indirectly supply fuel that has been substantially vaporized to an engine for subsequent combustion, thus reducing or eliminating the need for excess fuel supply during cold start and warm up conditions. In addition, at normal operating temperatures of the engine, the air-fuel mixture can be controlled in such a way that virtually all of the fuel is effectively burned, thus reducing emissions. In a preferred embodiment, the apparatus of the present invention is used with a supply of liquid fuel that supplies liquid fuel, at least one capillary flow passage connected to the liquid fuel supply, and a heat source connected along the at least one capillary flow passage. The heat source can be operated to heat liquid fuel in the at least one capillary flow passage sufficiently to supply a substantially vaporized fuel stream that can optionally contain a smaller proportion of the heated liquid fuel that has not been vaporized. The fuel vaporization device is preferably operated to supply a stream of vaporized fuel to the application. The invention also provides a method for supplying fuel to an application for subsequent combustion, including the steps of supplying a liquid fuel to at least one capillary flow passage, and heating the liquid fuel in at least one capillary flow passage sufficiently to causing a substantially vaporized fuel stream to be supplied to the application. A fuel vaporization system in accordance with the present invention includes at least one capillary size flow passage through which a liquid fuel flows before its feeding to a combustion application. The heat is applied along the capillary passage which results in at least a part of the liquid fuel entering the flow passage being converted to vapor as it travels along the passage. The fuel leaves the capillary passage in the form of vapor which may optionally contain a smaller proportion of heated liquid fuel that has not been vaporized. By "substantially vaporized", we understand that at least 50% of the liquid fuel is vaporized by the heat source, preferably at least 70%, and most preferably at least 80% of the liquid fuel. The vaporized fuel can be mixed with air to form an aerosol having an average size of small droplets of 25 μm or less, preferably 10 μp? or less, and more preferably 5 um or less. The capillary-sized fluid passage is preferably formed in a capillary body such as a metal, ceramic or glass single-layer or multi-layer body. The passage has an enclosed volume that opens to an entrance and an exit any of which may be open towards the exterior of the capillary body or may be connected to another passage within the same body or another body or to attachments. Since it is preferred to minimize the thermal inertia, the heater can be formed by a portion of the body such as a section of stainless steel pipe or the heater can be a discrete layer or a wire of heat-resistance material incorporated within the capillary body or on said body. The fluid passage can have any shape that has an enclosed volume opening to an inlet and outlet and through which a fluid can pass. The fluid passage can have any desired cross section with a preferred cross section being a circle of uniform diameter. Other capillary fluid passage cross sections include non-circular shapes such as triangular, rectangular, square, oval, or other shapes, and the cross section of the fluid passageway need not be uniform. The fluid passage may extend in a rectilinear or non-rectilinear manner and may be a single fluid passage or a multipath fluid passage. In the case in which the capillary passage is defined by a metallic capillary tube, the tube can have an internal diameter of 0.01 to 3 mm, preferably 0.1 to 1 mm, more preferably 0.15 to 0.5 mm. Alternatively, the capillary passage can be defined by its cross-sectional area of the passage which can be 8 x 10"5 to 7 mm", preferably 8 x 10"3 to 8 x 10" 1 mm2 and more preferably 2 x 10"'to 23 x 10" 1 mm2. Many combinations of single or multiple capillaries, various pressures, various lengths of capillaries, amounts of heat applied to the capillary, and different shapes and areas in cross section are suitable for a given application. The capillary tube is also characterized because it has a low thermal inertia. By "low thermal inertia", we understand that the body to be heated (the capillary tube) has a sufficiently low mass in such a way that it requires a minimum time to warm up to the operating temperature. As preferred, the capillary passage can be brought to the desired temperature to vaporize the fuel rapidly, preferably within 2.0 seconds, more preferably within 0.5 second and most especially within 0.1 second, which is beneficial in applications in which a delay to reach the desired temperature would be undesirable as for example during cold start and heating conditions. In addition, low thermal inertia can provide advantages during the normal operation of an application, such as by improving the response of the application to sudden changes in energy requirements. In one embodiment, the present invention provides a method and apparatus for preparing fuel for liquid fuel combustion applications. A combustion application is found at very low liquid fuel flow rates, for example, lower than 0.1 grams per second, associated with combustion applications where other combustion preparation devices such as swirl atomization under conventional pressure or atomization by air jets have proven to be undesirable or inadequate. The device can generate fuel vapor and / or fuel aerosols that have extremely small droplet diameters in flow regimes within a range of a few tens of watts to several thousand watts of chemical energy. Multiple capillaries can be used in parallel to increase the total production of chemical energy for use with larger combustion applications. The device can produce ultra fine fuel aerosol and / or vapors, which are ideal for preparing homogeneous fuel / air mixtures for clean and efficient combustion in compact combustion systems, and exhibit excellent ignition characteristics. Advantageously the apparatus of the present invention can operate at low fuel supply pressure (7.0 kg-m / sec (100 psig) or less) eliminating the need for high-pressure pumps that consume energy, are heavy, and cost elevated, such as the pumps that are required to supply fuel at or near the supercritical pressure of the fuel. In the same way, the apparatus of the present invention does not require higher air supply pressures or that eliminates the need for heavy air movers that consume energy. The apparatus can also be used to provide pilot lights activated by liquid fuel for boilers, water heaters, and the like, and can perform a wide range of non-traditional liquid fuel applications. An advantage of the apparatus in accordance with the present invention is its ignition energy requirement characteristics. The minimum ignition energy is a term used to describe the ease with which an atomized fuel / air mixture can be ignited, typically with a lighter, such as a spark ignition source. The device according to the present invention can provide a vaporized fuel and / or aerosol with small droplets having a Sauter Mean Diameter (SMD) less than 25 um, preferably less than 10 μm and more preferably less than 5 μm, such fine aerosols are useful for improving the burning characteristics and stability of flame in gas turbine and other combustion applications. Also, very significant reductions in the minimum ignition energy can be achieved to produce those with SMD values of 25 μp? or less. For example, in accordance with the comments in Lefebvre, Gas Turbine Combustion (Hemisphere Publishing Corporation, 1983) on page 252,; r, iP., a term that correlates with the ease with which a mixture of atomized fuel / air can be ignited, decreases rapidly as the SMD decreases. The minimum ignition energy is approximately proportional to the Sauter Medium Diameter (SMD) tube of small aerosol fuel droplets. SMD is the diameter of a small droplet whose surface to volume ratio is equal to that of the entire spray and refers to the mass transfer characteristics of the spray. The relationship between Emin and SMD for various fuels is shown in Lefebvre as being obtained approximately through the following relationship:
Lcg = 4.5 (log SMD) + k; where? · .. is measured in rv.J, SMD is measured in um and k is a constant related to the type of fuel. According to Lefbvre, a heavy fuel oil has a minimum ignition energy of approximately 800 mj at a SMD of 115 μ? and a minimum ignition energy of approximately 23 mJ to a 50 μm SMD. Issoctane has a minimum ignition energy of approximately 9 mJ at a SMD of 90 μm and a minimum ignition energy of approximately 0.4 mJ at a SMD of 40 μp ?. For a diesel fuel, when the SMD is equal to 100 μ ??, Emm is approximately 100 mJ. A reduction of SMD to 30 um would provide a reduction of?, T ?. at approximately 0.8 mJ. As can be seen, the requirements of the ignition system are substantially reduced in the field of SMD values below 25 um. It has been determined that the mass flow regime of liquid fuel through a capillary flow passage depends on the pressure of the liquid fuel that enters the capillary flow passage and the amount of heat that is applied to the capillary flow passage . The amount of vapor and the size of the small fuel droplets also depend on these two variables as discussed below, as well as the environment where the stream of vaporized fuel flows. The fuel vaporization device of the present invention can be adapted for virtual use all applications requiring a substantially vaporized fuel stream by varying the length of the capillary flow passage, the cross-sectional area of the capillary flow passage, the number of capillary flow passages that are used, the pressure of the fuel supplied to the capillary flow passage and / or the amount of heat that is supplied to the capillary flow passage. It will be observed by persons with knowledge in the art that an empirical alteration of these variables will provide an adequate configuration for virtually any application that requires a source of heat. It is contemplated that various pressures below 7.0 kg-m / sec (100 psig), or up to 3.5 kg-m / sec (50 psig), or less may be applied to the liquid fuel source. Alternatively, no pressure source may be applied to the liquid fuel source in the case of gravity-fed applications. In applications where fuel-air mixtures are ignited near the output of a fuel vaporization device, the characteristics of combustion emissions are sensitive to the quality of distribution of small sizes of fuel droplets. Fine sprays of high quality promote fuel evaporation and improve mixing, thus reducing the tendency to rich combustion and the associated generation of smoke and soot. It is known that small fine droplets evaporate rapidly and also follow the flow lines and therefore have no tendency to impact against the walls of the burner. Conversely, larger droplets may not follow the flow lines and may impact the burner walls and cause emissions of CO-hydrocarbon and carbon deposits (coking). This problem is most noticeable in systems in which flames are highly confined. Accordingly, the fuel degassing device of the present invention is beneficial in these applications due to its ability to produce a vaporized fuel stream and / or an aerosol of very fine droplets that have a much lower tendency to impact on burner walls. In applications in which fuel is directed to a combustion chamber through an air flow, such as through the use of a manifold, it has been found that sizes of small aerosol droplets that are too large to be transported by a current of air until the deflection of the air current through a surface such as the wall of a manifold, at that point the small drops hit the surface and accumulate on the wall. Depending on the type of fuel, small droplets larger than 25 um can impact deviating surfaces. Since a certain amount of fuel accumulates on the surface of the flow passage, an additional amount of fuel must be injected to supply and sufficient fuel vapor to the application for ignition to occur. Finally, the accumulated fuel is burned incompletely and escapes as unburned fuel and pollutants. In contrast, the capillary flow passage in accordance with the present invention can offer an aerosol having a substantial amount of small aerosol droplets of minute size which is beneficial insofar as small aerosol droplets can be transported by an air current, independently of the flow path, in the application and burned efficiently with very low emissions. During the vaporization of the liquid fuel in a heated capillary passage, carbon deposits and / or heavy hydrocarbons can accumulate in the walls of the capillaries and the flow of the fuel can be severely restricted, which can finally cause the clogging of the flow passage capillary. The speed at which these deposits accumulate depends on the temperature of the capillary wall, the speed of the fuel flow and the type of fuel. It is believed that fuel additives can be useful in reducing such deposits. However, if a tamponade develops, said plugging can be cleaned by oxidation of the deposits. Figure i presents an apparatus 10 for vaporizing a liquid fuel taken from the liquid fuel source, in accordance with the present invention. The apparatus 10 includes a capillary flow passage 12, having an inlet end 14 and an outlet end 16. A fluid control valve 18 is provided to position the inlet end 14 of the capillary flow passage 12 in a communication of fluid with a source of liquid fuel F and for introducing the liquid fuel in a substantially liquid state in capillary flow passage 12. As preferred, a fluid control valve 18 can be operated by solenoid 28. A heat source 20 it is placed next to the capillary flow passage 12. As is especially preferred, a heat source 20 is provided by forming the capillary flow passage 12 from a tube of electrically resistive material, a capillary flow passage portion 12. forming a heater element when an electric current source is connected to the tube at connections 22 and 24 to supply current there. The heat source 20, as can be seen, is then operated to heat the liquid fuel in the capillary flow passage 12 to a level sufficient to change at least a part thereof from the liquid state to a vapor state and to supply a fuel stream substantially vaporized from the outlet end 16 of the capillary flow passage 12. The apparatus 10 also includes a device for cleaning deposits formed during the operation of the apparatus 10. The device for cleaning deposits shown in Figure 1 includes a fluid control valve 18, a heat source 20 and an oxidant control valve 26 for placing the capillary flow passage 12 in fluid communication with an oxidant source C. As can be seen, the oxidation control valve can be located at or near any capillary flow passage end 12 or it may be configured to be in fluid communication with end portion of the capillary flow passage 12. If the oxidant control valve is located at or near the outlet end 16 of capillary flow passage 12, it then serves to place the source of oxidant C in fluid communication with the end of the flow outlet 16 of the capillary flow passage 12. In operation, the heat source 20 is used to heat the oxidant C in the capillary flow passage 12 to a level sufficient to oxidize the deposits formed during the heating of the liquid fuel F. In one embodiment, to pass from a supply mode of fuel to a cleaning mode, the oxidizer control valve 26 serves to alternate between the introduction of the liquid fuel F and the introduction of oxidant C into the capillary flow passage 12 and to allow in situ cleaning of the capillary flow passage when the oxidant is introduced into said at least one capillary flow passage. A technique to oxidize deposits includes the passage of air or steam through the capillary. The flow passage is preferably heated during the cleaning operation in such a way that the oxidation process starts and continues until the deposits are consumed. To increase this cleaning operation, a catalytic substance can be used, either as a coating on the capillary wall or as a component of said capillary wall to reduce the temperature and / or the time required to achieve cleaning. In the case of a continuous operation of the fuel supply system, more than one capillary flow passage can be used in such a way that when a clogging condition is detected, for example by the use of a sensor, the fuel flow can be diverted to another capillary flow passage and the flow of oxidant can be initiated through the capillarized capillary flow passage that must be cleaned. By way of example, a capillary body may include several capillary flow passages there and a valve arrangement may be provided to selectively supply the liquid fuel or air to each flow passage.
Alternatively, the fuel flow can be diverted from a capillary flow passage and initiated oxidizer flow at pre-set intervals. The supply of fuel to a capillary flow passage can be effected through a controller. For example, the controller can activate the fuel supply for a preset period of time and deactivate the fuel supply after the preset time period. The controller may also adjust the pressure of the liquid fuel and / or the amount of heat supplied to the capillary flow passage based on one or more detected conditions. The detected conditions may include, inter alia: fuel pressure; the capillary temperature, and the air-fuel mixture. The controller can also control several fuel supply devices connected to the application. The controller can also control one or several capillary flow passages to clean deposits or clogging. For example, cleaning a capillary flow passage can be accomplished by applying heat to the capillary flow passage and by supplying a flow from an oxidant source to the capillary flow passage. The cleaning technique can also be applied to fuel vaporization devices that must operate continuously. In this case, multiple capillary flow passages can be employed. A fuel vaporization device of multiple example capillary flow passages of the present invention is illustrated in Figures 2 and 3. Figure 2 presents a schematic view of an array of multiple capillary tubes integrated in a single assembly 94. The Figure 3 presents an end view of the assembly 94. As shown, the assembly may include the three capillary tubes 82A, 82B, 82C and a positive electrode 92 may include a solid stainless steel rod. The tubes and the rod can be supported on a body 963 of electrically insulating material and energy can be supplied to the rod and capillary tubes through attachments 98. For example, direct current can be supplied to the ends upstream of one. or several of the capillary tubes and a connection 95 at the ends downstream thereof can form a return path for a current through the rod 91. Reference is now made to Figure 4, wherein a multi-tube system capillaries 80 includes capillary tubes 82A to C, fuel supply lines 84A to C, oxidant supply lines 86A to C, las. oxidizing control valves 88A to C, energy drain lines 90A-C and common ground 92. System 80 allows the cleaning of one or more capillary tubes while the fuel supply continues with one or several toros capillary tubes .
For example, combustion of fuel through the capillary flow passages 82B, 82C can be effected during cleaning of the capillary flow passage 82A. The cleaning of the capillary flow passage 82A can be achieved by closing the fuel supply to the capillary tube 82A, supplying air to the capillary flow passage 82A, with sufficient heating to oxidize the deposits in the capillary flow passage. Thus, the cleaning of one or several capillaries can be carried out while continuously supplying fuel. The capillary flow passage or the various capillary flow passages that are being cleaned are preferably heated during the cleaning process through an electric resistance heater or thermal feedback of the application. Again, the period of time between the cleanings for any given capillary flow passage can be set either based on the known characteristics of tamponade determined experimentally or else a detection and control system can be used to detect the accumulation of deposits and for Start the cleaning process as required. The supply of fuel to a capillary flow passage can be controlled through a controller. For example, the controller can activate the fuel supply to an application, for example, a spark-ignited internal combustion engine, a diesel engine, a burner, a Stirling engine, a gas turbine engine, etc., when the operation of the application is about to start and deactivate the fuel supply after a pre-established time lapse or when a signal is received to deactivate the application. The controller may also adjust the pressure of the liquid fuel and / or the amount of heat supplied to the capillary flow passage based on one or more conditions detected. The detected conditions may include, inter alia: the pressure of a multiple; the fuel pressure; the capillary temperature, the application temperature, and the air-fuel mixture in the exhaust outlet. The controller can also control multiple fuel vaporization devices connected to the application. The controller can control one or several capillary flow passages to clean deposits or clogs there. For example, the controller can control more than a capillary flow passage to clean deposits or clogs there for a continuous operation of the application. The controller can divert the fuel flow from a partially capped capillary flow passage to one or more other capillary flow passages and initiate a flow of oxidizing gas and heat to the partially capped capillary flow passage until the capillary flow passage is clean of deposits. Figure 5 shows an exemplary scheme of a control system for operating a combustion system incorporating a supply of oxidizing gas to clean clogged capillary passages in accordance with the invention. The control system includes a controller 100 operably connected to a fuel supply 102 that supplies fuel and optionally feeds air to a flow passage, for example, a capillary tube 104. The controller is also operatively connected to a supply of energy 106 that supplies power to a resistance heater or directly to a metal capillary tube 104 to heat the tube sufficiently to vaporize the fuel. If desired, the combustion system can include multiple flow passages and heaters operatively connected to the controller 100. The controller 100 can be operatively connected to one or more signaling devices, for example an ignition switch. off, thermocouple, fuel flow rate sensor, air flow rate sensor, power output sensor, battery charge sensor, etc., so the controller 100 can be programmed for an automatic control operation of the combustion system in response to the signal (s) sent to the controller by the signaling devices. In operation, the device according to the present invention can be configured to feed back the heat produced during combustion to heat the liquid fuel sufficiently to vaporize substantially the liquid fuel as it passes through the capillary which reduces or eliminates or complements the need for electrical or other heating of the capillary flow passage. For example, the capillary tube may be longer to increase the surface area thereof for greater heat transfer, the capillary tube may be configured to pass through the combustion fuel, a heat exchanger may be placed to use the gas from escape of the combustion reaction to preheat the fuel, etc. Figure 6 shows, in specified form, how a capillary flow passage 64 can be positioned such that a liquid fuel moving therein can be heated to an elevated temperature in order to reduce the energy requirements of the heater to vaporize the fuel. As shown, a portion 66 of a tube comprising a capillary flow passage passes through the flare 68 of the burned fuel. For initial start-up, a resistance heater comprising a section of the tube or a separate resistance heater heated by electrical conductors 70, 72 connected to a power source, for example, a battery 74 may be used to initially vaporize the liquid fuel. After the ignition of the vaporized fuel through a suitable ignition arrangement, the portion 66 of the tube can be preheated by the heat of combustion in order to reduce the energy otherwise required for a continuous vaporization of the fuel by the heater. resistance. A) Yes, by preheating the tube, the fuel in the tube can be vaporized without using the resistance heater so that energy can be saved. As will be seen, the apparatus and system for preparing and supplying fuel illustrated in Figures 1 to 6 can also be used in relation to another embodiment of the present invention. Referring again to Figure 1, the means for cleaning deposits includes a fluid control valve 28 and a solvent control valve 26 (before the oxidizer control valve 26 in the embodiment employing oxidation cleaning) to place the capillary flow passage 12 in fluid communication with a solvent, the solvent control valve 26 is positioned at one end of the capillary flow passage 12. In the embodiment of the apparatus employing solvent cleaning, the solvent control valve alternates between the introduction of liquid fuel and the introduction of bladder in capillary flow passage 12, allowing cleaning in. site of the capillary flow passage 12 when the solvent is introduced into the capillary flow passage 12. While a wide range of solvents are useful, the solvent may comprise liquid fuel from the liquid fuel source. When this is the case, no solvent control valve is required, since there is no need to alternate between fuel and solvent, and the heat source must be removed over time or deactivated during the passage cleaning process. capillary flow 12. Figure 7 presents another example embodiment of the present invention. An apparatus 200 has a capillary flow passage 212 for supplying liquid fuel F to an application. Details of the capillary flow passage 212 for supplying fuel are illustrated through Figure 7A. As shown therein, an axially movable rod 232 is positioned within the capillary flow passage 212. The outlet end 216 of the capillary passage 212 is widened and the rod end 232 is tapered to form a valve where the axial movement of the Rod 232 opens and closes the valve. Within the tube there are also brushes 234 for cleaning the axial movement rod 232 as it travels reciprocatingly within the capillary flow passage 212. According to another embodiment of the present invention, the fuel vaporization device is supplied with a substantially vaporized fuel. which can be mixed with air at room temperature, produced in the air supply passages leading to a combustion chamber of the application. Alternatively, the vaporized fuel can be mixed with air that has been preheated, for example through a heat exchanger, which preheats the air with the heat of the exhaust gases removed from a combustion chamber of the application. If desired, the air can be pressurized, for example, through a blower before being mixed with the vaporized fuel. If desired, the fuel vaporization method and device of the present invention can be used in any application or apparatus that requires a stream of vaporized fuel. For example, these applications include, but are not limited to, water heaters and boilers, portable heaters, energy conversion devices, internal combustion engines, refrigerators, fuel processors or reformers, external combustion engines, gas turbines, cells. of fuel, direct thermal conversion devices, etc. The present invention can also be applied to applications where it is desirable to burn the liquid fuel cleaner. EXAMPLES Example 1 Tests were carried out in which a JP 8 jet fuel was vaporized by supplying the fuel to a capillary passage heated at constant pressure with a diaphragm micropump system. In these tests, capillary tubes of different diameters and lengths were used. The tubes were constructed of stainless steel 304 with lengths of 2.5 to 7.6 cm (1 to 3 inches) and with internal diameters (ID) and external diameters (OD), in cm (inch), following: 0.025 ID / 0.046 OD ( 0.010 ID / 0.018 OD), 0.033 ID / 0.083 OD (0.013 ID / 0.033 OD), and 0.043 ID / 0.064 OD (0.017 ID / 0.025 OD). The heat for the vaporization of the liquid fuel was generated by the passage of an electric current through a part of the metal tube. The decrease in sizes of small droplets was measured using a Spray-Tech laser diffraction system manufactured by Malvern. Small droplets with a Sauter Mean Diameter (SMD) between 1.7 and 4.0 um were produced. The SMD is the diameter of a small drop employing surface and volume proportions equal to that of an entire spray and refers to the mass transfer characteristics of the spray. Example 2 Tests were carried out to demonstrate the benefits of the oxidation cleaning technique in a heated capillary flow passage using a sulfur-free, non-additive gasoline, which is known to produce high levels of deposit formation. The capillary flow passage used for these tests was a heated 2-inch long stainless steel capillary tube having an internal diameter of 0.058 cm (0.023 inches). The fuel pressure was maintained at 0.7 kg / crtr (10 psig). The capillary was supplied with energy to achieve various levels of R / R0; where R is the capillary resistance and R0 is the capillary resistance under ambient conditions. Figure 8 presents a graph of fuel flow rate versus time. As shown, for this gasoline that does not contain detergent additive, an important tamponade was observed in a very short time lapse with urra loss of 50% of the flow regime observed in 10 minutes. After presenting a substantial plugging, the fuel flow was discontinued and air was replaced at 0.7 kg / cnr (10 psig). Warming was provided during that period and, a minute later, a significant cleanup was achieved, with the flow regimes returning to previous levels. EXAMPLE 3 This example demonstrates that the plugging is much less severe in the heated capillary flow passage of Example 2, when a commercial grade gasoline is used with a package of effective additives. As shown in Figure 9, a reduction of less than 10% was shown in terms of the fuel flow rate after an operation of the device of almost four hours. Example 4 To compare various gasolines and the impact of detergent additives on the corking, five test fuels were used in the heated capillary flow passage of Example 2. The fuels tested included an additive base gasoline containing 300 ppm sulfur. , a base gas without additive and without sulfur, the base gas without sulfur with a commercially available additive (additive A) and the base gas without sulfur with another commercially available additive (additive B). As shown in Figure 10, fuels with additives performed similarly while fuels without additives presented severe packing in less than one hour of operation. Example 5 This example compares the operation over time of a capillary flow passage operating in an aircraft fuel without additive (JP-8) to the same capillary flow passage that operates with No. 2 diesel without additive operated in a capillary flow passage having a diameter of 0.036 cm (0.014 inches) and a th of 5.1 cm (2 inches). The fluid pressure was adjusted to 1.1 kg / cnr (15 psig). Energy was fed to the capillary to achieve a R / Rc level of 1.19; where R is the heated capillary resistance and R is the capillary resistance under ambient conditions. As shown in Figure 11, fuels performed similarly in the first ten minutes of operation, and diesel fuel presented a more severe plugging later. Example 6 Tests were carried out to evaluate the efficiency of the technique of cleaning by oxidation in the heated capillary flow using a No. 2 diesel fuel without additives which is known to produce high levels of deposit formation. The capillary flow passage used for these tests was a 5.1 cm (2 inch) long heated capillary tube constructed of stainless steel, having an internal diameter of 0.036 cm (0.014 inches). The fuel pressure was maintained at 1.1 kg / cnr (15 psig). The capillary was supplied with energy to achieve a R / R0 level of 1.19; where R, again, is the heated capillary resistance and Rc is the capillary resistance under ambient conditions. Figure 12 presents a graph of the fuel flow rate versus time. As shown, for this fuel that does not contain detergent additive, a significant plugging occurred in a very short time with a 50% loss of the flow regime observed in approximately 35 minutes of continuous operation. In the second experiment, after five minutes of operation, the fuel flow was discontinued and air was replaced at 0.7 kg / cm £ (10 psig) for a period of five minutes. Warming was also provided during this period. This procedure was repeated every five minutes. As shown in figure 12, the oxidation cleaning process increased the fuel flow rate in virtually all cases and presented a tendency to encourage the overall decrease of the fuel flow regime over time. However, the efficiency of the process was relatively lower than what was achieved using a gasoline without additives, in accordance with that described in example 2. Example 7 Tests were carried out to evaluate the effect of a detergent additive anti-fouling grade with the diesel fuel No. 2 of Example 6 on the fuel flow rate over time in a heated capillary flow passage. The capillary flow passage used for these tests, again, was a 5.1 cm (2 inch) long heated capillary tube constructed of stainless steel, having an internal diameter of 0.036 cm (0.014 inches). The fuel pressure was maintained at 1.1 kg / cnr (15 psig) and power was fed to the capillary to achieve 2
a level of?, / R. from 1.19. Figure 13 presents a comparison of fuel flow rate versus time for diesel fuel No. 2 with additives and a diesel fuel without additives. As shown, in the case of fuel that does not contain detergent additive, significant plugging was observed in a very short period of time, with a quality of 50% of the flow regime observed in approximately 35 minutes of continuous operation, while the The same base fuel that contained the detergent presented a much less significant clogging over an extended period of time. Even though illustrative modalities have been shown and described, a wide range of modifications, changes and substitutions can be made to the prior disclosure and in some cases, some features of the modality may be employed without corresponding use of other features. Accordingly, it is appropriate that the appended claims be considered broadly and in a manner consistent with the scope of the embodiments disclosed herein.